As the electronics industry advances, and production of light weight components increases, the development of new materials gives producers increased options for further improving the performance and ease of manufacture of such components. Materials used in the manufacture of electronic components include the resin required for the preparation of prepregs (which are, in turn, used for the preparation of multilayered printed circuit boards and printed wiring boards), resins used for the preparation of solder masks (which define solder areas on the multilayered printed wiring board), and resins used for preparation of glob top (which protects microelectronic devices from the environment).
Multilayered printed circuit boards are currently produced mainly by (a) a mass laminating technique and (b) a pin laminating technique. In these techniques, a printed circuit board for inner layer use (hereinafter, referred to as “inner-layer board”) is first manufactured. This inner-layer board is combined with prepregs and then a copper foil or a single-side copper-clad laminate and the superimposed laminating materials are laminated to give a multilayered board, both sides of which are covered by a copper coating. This multilayered structure is processed as appropriate to form through-holes, outer-layer printed circuits, etc.
The initial manufacture of resins used in laminates is usually conducted by chemical producers and supplied to the trade in a workable form. Addition of a curing agent or catalyst, as well as optional components such as diluents, flow promoters, fire retardants, and other modifying resins is typically performed by the user. This may be done in the interest of customization to the application or to ensure that pre-reaction of the formulation does not occur.
Another common use of resins in the electronics industry is for the preparation of solder masks. Solder mask is used to prevent excessive flow of solder in plastic packages. The material used must maintain the integrity of the physical, chemical, mechanical, and environmentally related properties of the package. Solder masks were originally intended to be used on printed wiring boards (PWBs) as an aid to manufacturing, reducing the need for touch-up after machine soldering, reducing solder consumption, and providing mechanical protection for the main portion of the circuitry.
The main type of solder mask employed in the art is the “liquid photoimageable” solder mask. There are three primary methods of applying this type of soldermask: flood screen-coating, curtain, and spray coating. Each method has both advantages and drawbacks. Screen coating, for example, is efficient in material usage, but through-holes may be plugged in the process. These holes must then be vacated during development. Curtain coating is also efficient, but it is a much slower process since only one side of a board can be coated at a time. Spray coating is the best method to accomplish complete fill and trace application, but this technique can result in substantial material losses (e.g., in the range of 10-30% waste).
Another common use of resins in the electronics industry is as a liquid encapsulant (also referred to as “glob top”), wherein an aliquot of resin material is used to encase a component to protect it from certain stresses and from exposure to the environment. To meet the industry's ever-increasing demand for device reliability, materials for encapsulant applications must meet increasingly stringent performance requirements. Such requirements include excellent moisture resistance, ionic purity, low dielectric constant and good thermal properties. In the absence of these properties, especially in the presence of moisture and ionic impurities, corrosion (and ultimately failure of the device) will likely occur.
Yet another common use of resins in the electronics industry is in the preparation of non-hermetic electronic packages. Examples of such packages are ball grid array (BGA) assemblies, super ball grid arrays, IC memory cards, chip carriers, hybrid circuits, chip-on-board, multi-chip modules, pin grid arrays, and the like. In these structures, moisture resistance is an important consideration, both in terms of handling during assembly and reliability of the finished part. For example, absorption of moisture during assembly frequently leads to “popcorning” (the release, sometimes violent, of absorbed moisture upon heating to solder reflow temperatures). The development of moisture resistant resins for use in the preparation of non-hermetic electronic packages would be of great benefit to the art.
For all these applications, the microelectronics industry continues to require new resins which are able to meet its varying demands. Accordingly, there is a need for the development of materials to address the requirements of this rapidly evolving industry.